T4 is usually pretty fast for processing customs and immigration, you can easily be off the plane and landside in 5 minutes if you have no checked luggage. Expect 30-45 minutes or so with bags depending on when your bags hit the belt.
Once you've got landside you can either take one of the circular shuttle buses around the loop to T2. Alternatively you can do what I do and just walk it. After a long flight it gets the blood pumping again and you get a nice view of all the activity on the ramp as you do the walk.
You'll have to cart your bags to T2 yourself though, I don't think you can drop them with AA/Qantas in T4.